You should always count the ongoing cost of software you buy for your business. You might pay less for a particular package, but if it takes a lot more time and effort to set up and maintain to do the job you want it to do, the long-term cost is more than other software that's easier to use. Even if that other software costs more up front, the lower maintenance costs will quickly overtake the "cheaper" option.
Mokalus of Borg
PS - Also, consider how rare and expensive are the skills needed for the software.
PPS - There are a lot of factors to consider.